The present invention relates in general to shaft seals, and in particular to a new and useful device for magnetically controlling a sealing gap in a shaft seal.
Shaft seals are known which provide substantial reduction in the supply of sealing fluid flowing along a wall by which two parts are separated from each other and which is needed for sealing a rotating part against a non-rotating one (German OS No. 21 34 964). The non-rotating seal ring is freely movable in every direction relative to the non-rotating part and is connected thereto by one or more deformable, leakproof walls.
What is disadvantageous in this design is that upon a clogging of the narrow supply bores, the resetting force may be nullified and the rotating ring might brush against the stationary ring.
To eliminate these drawbacks, German OS No. 24 44 544 teaches to direct the sealing gas into the sealing gap through spiral grooves which are provided either in the rotating or in the non-rotating seal ring, from the outside inwardly, considered in the radial direction, whereby gas-dynamic resetting forces are produced. The disadvantage of this design is that the resetting forces depend on the rotational speed and that at low speeds, an additional static gas cushion produced through throttling bores must be provided.
To reduce working fluid leakage in turbo machines, German OS 25 15 316 seaks to keep the shaft seal in concentric position relative to the shaft by means of an electronically controlled magnetic field produced by solenoids. Nothing is disclosed about a design as a radial gap seal in connection with the concentric position relative to the shaft.
Another idea is suggested in German OS No. 16 75 354, namely of adjusting the sealing gap by utilizing the repulsive force of permanent magnets embedded in the seal ring between the throttling bores. However, no details of such a design are given.
The prior art constructions are not suitable for extremely narrow sealing gaps in radial shaft seals which, in addition to the sealing fluid, are exposed to elastic resetting forces acting on the non-rotating seal ring, since with a superimposition of the forces acting axially on the seal gap, the needed uniformity of the gap is not ensured and the ring rotating with the shaft may come into contact with the non-rotating ring.